Steam injection method for producing oil



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Fr-fnu QQ. 395249502 Aug. 18, 1970 R. L.. sLoAN STEAM INJECTION METHODFOR PRODUCING OIL Filed Feb. s, 1969 I NVENTOR.`

NOLLOBNI NVZ-ILS WOUzI NOLLVHfLLVS HBLVM 7 United States Patent C)3,524,502 STEAM INJECTION METHOD FOR PRODUCING OIL Richard L. Sloan,Houston, Tex., assignor to Tenneco Oil Company, Houston, Tex. acorporation of Delaware Filed Feb. 3, 1969, Ser. No. 795,831 Int. Cl.E21b 43/24 U.S. Cl. 166-250 4 Claims ABSTRACT OF THE DISCLOSURE Themethod of steam injection and producing a hydrocarbon bearing formationpenetrated by a well bore t achieve optimum steam soak. The methodincludes injecting a predetermined quantity of water as steam into thewell bore followed by logging of the well bore to determine the percentof liquid saturation of the formation adjacent the well bore. Thereafteroil is produced from the formation for a predetermined period of timeand the quantity of oil produced is compared with the amount of oilrecovered. The foregoing steps are repeated with the saturation level ofthe formation being increased to an optimum level where the rate ofincrease of units of oil recovered per unit of water injected as steamstarts to decline.

This invention relates to a method of steam injecting and producing ahydrocarbon bearing formation penetrated by a well bore to achieveoptimum steam soak. More particularly, this invention relates to amethod of determining optimum steam soak cycle in a steam injectionprocess for the recovery of oil from the formation.

Certain formations have heavy oil deposits, as for example some inCalifornia which are readily adaptable to steam stimulation treatments.One of the unknown factors is the length of time needed or the amount ofwater (as steam) required to adequately treat a formation.

Prior methods for judging the size of steam slugs are trial and error orbased on experience. For example, a particular well penetrating aformation is given a steam treatment and a productivity thereafterdetermined. An adjacent well is thereafter injected with a smaller orlarger slug of steam and the productivity thereof compared with thefirst well. This trial and error method may be continued until someoptimum level of saturation is determined, but the results are aninexact method of measurement resulting in error in many instances.

It is therefore an object of this invention to provide an improvedmethod of steam injecting and producing a hydrocarbon bearing formationpenetrated by a Iwell bore to achieve optimum steam soak.

It is also an object of this invention to provide an improved method forobtaining the optimum steam soak for one well penetrating a formationand applying the optimum steam soak level to adjacent wells penetratingthe formation.

Briefly stated, this invention is for a method of steam injecting andproducing a hydrocarbon bearing formation penetrated by a well bore toachieve optimum steam soak. The method includes the steps of injecting aslug of steam of a predetermined amount into the formation. Thereafterthe formation is logged to measure the percent of fluid saturationthereof. Hydrocarbons are then produced from the formation for apredetermined period of time. These steps of injection, logging, andproducing are repeated at least until the liquid saturation of theformation adjacent the well bore reaches a level where the rate ofincrease of hydrocarbons recovered per unit of steam injected startsdeclining. This optimum level is established by comparing the quantityof oil produced during the production step with the quantity of steaminjected during the injection step.

3,524,502 Patented Aug. 18, 1970 ICC ln certain embodiments of theinvention, adjacent well bores penetrating the formation may alsosubsequently be steam injected until the liquid saturation of theformation adjacent thereto reaches a saturation level at least equal tothe optimum saturation level for the iirst well, and the producing oilfrom the other well bores.

Reference to the drawing will further explain the invention:

The drawing is a graph on which is plotted on the horizontal axisnumbers representing the ratio between the units of oil produced to theunits of water (as steam) injected during the injecting cycle.

The vertical axis shows the percent of liquid or water saturation of thewell bore as the steam injecting steps are repeated. The curvedesignated by the numeral 10 is a typical curve for a well bore treatedin accordance with the teaching of this invention, with the optimumpoint 11 showing the point at which the rate of increase of units of oilrecovered per unit of steam injected starts to decline, which point willsometimes hereinafter be referred to as the optimum liquid saturationlevel.

In carrying out the teachings of this invention, let it be assumed thata hydrocarbon bearing formation, such as a heavy oil bearing formationsuch as those found in California, is penetrated by plurality of spacedapart well bores.

One of the well bores may be selected as the test well and initiallylogged to determine the liquid saturation of the oil bearing formationadjacent thereto. This logging may measure either hydrocarbon and/ orIwater saturation.

Thereafter, a predetermined quantity of water as steam is injected intothe test well and into the oil bearing formation to thereby heat thesame. Then either during or subsequent to said injecting step, the wellbore is logged again to measure the fluid saturation of the formation.Then oil is produced from the formation for a predetermined period oftime. The quantity of oil produced during the production step iscompared with the quantity of steam projected during the injection step.

The foregoing steps are repeated until the liquid saturation of theformation adjacent the test well bore reaches an optimum level. Thisoptimum level is the point at which the rate of increase of units of oilrecovered per unit of water as steam injected into the test well startsdeclining.

The line 10 on the drawing is a plot of steam induced Water saturationand the amount of oil recovered per barrel of steam injected. Thus,there is established an efliciency and economic perimeter. The more oilrecovered per barrel of steam injected the better the economics. Anoptimum is shown at point 11 whereafter a small additional increment ofoil would be recovered while increasing the induced water saturation anadditional 20 percent. From an economic standpoint, the additional oilrecovered may not have a value equivalent to the cost to inject theadditional steam, plus the delayed income from not placing the well backon production in a shorter length of time, plus the incremental cost toseparate the additional water from the oil and the surface treatingfacilities. Based on the localized proven results in the test well, theother adjacent well bores are then steam injected to the optimumsaturation level established for the test well.

It is to be understood that the method of logging the well borecontemplated by this invention may be with a conventional logging toolwhich is arranged to measure the liquid saturation thereof either interms of hydrocarbons and/or water saturation. Hence, there is provideda method of determining optimum steam soak cycle in a hui and puff steaminjection process. There is thus provided a method designed to providerapid, accurate measure of oil and/or water saturation to prescribe thesize of a steam stimulation treatment to be administered to a given welland ultimately to the entire formation. Prior t injecting steam, alogging tool capable of measuring hydrocarbon and/or water saturation ina reservoir may be run and the initial oil and/or Water contentdetermined. The reservoir may then be steamed, allowed to soak andlogged again. After being placed on production, the Well is loggedagain. By logging and determining the oil and/ or Water saturation,optimum steam and soak cycles can be determined.

It is to be understood that any conventional logging technique(electrical, nuclear, or the like) is acceptable, if it is possible todetermine uid saturations therefrom. A one well test should establishoptimum saturation levels at different cycles of treatment. Any methodof saturation measurement is acceptable as long as it is possible to logduring, or immediately following, the steam injection cycle of the huffand puff process.

It is to be understood that the examples discussed above are merelyillustrative of the invention.

What is claimed is:

1. The method of steam injecting and producing a hydrocarbon bearingformation penetrated by a well bore to achieve optimum steam soak, saidmethod comprising the steps of:

injecting a slug of steam of a predetermined amount into saidformation;l

logging said formation to measure the percent of uid saturation thereof;

producing hydrocarbons from said formation` for a predetermined periodof time after said injection step; repeating said injection, logging andproduction steps; and continuing said repeating of said steps at leastuntil the liquid saturation of said formation reaches a level where therate of increase of units of hydrocabons recovered per unit of steaminjected starts declining.

2. The method of determining optimum steam soak cycle in a steaminjection process for the recovery of oil from a formation, thecombination of steps comprising:

injecting a predetermined quantity of water as steam into said formationthrough a well bore penetrating said formation;

logging said bore to determine the percent of liquid saturation of saidformation adjacent said well bore; producing oil from said formationthrough` said well bore for a predetermined period of time;

comparing the quantity of oil produced during said production step withthe quantity of steam injected in said injecting step;

and continuing repeating said injecting, logging, producing andcomparing steps at least until the liquid saturation of said formationadjacent said well bore reaches an optimum level where the rate ofincrease of units of oil recovered per unit of water injected as steamstarts declining.

3. The invention as claimed in claim 2 including the additional steps ofinjecting steam into a plurality of other well bores penetrating saidformation until the liquid saturation of the formation adjacent each ofsaid other Well bores reaches a saturation level at least equal to saidoptimum saturation level established for said first well bore;

and producing oil from said other well bores.

4. In a method of steam-injecting and producing a hydrocarbon bearingformation penetrated by a plurality of Well bores to achieve optimumsteam soak, the combination comprising the steps of:

injecting a slug of steam of a predetermined amount into said formationthrough one of said well bores; logging said one well bore to measurethe percent of uid saturation thereof; producing hydrocarbons from saidformation through said one well bore for a predetermined period of timeafter said injection step; repeating said injection, logging andproduction steps; continuing said repeating of said steps at least untilthe liquid saturation of said formation reaches an optimum level wherethe rate of increase of units of hydrocarbons recovered per unit ofsteam injected starts declining; injecting steam into said other wellbores until the liquid saturation of said formation adjacent thereto isat least equal to the optimum liquid saturation of said one well bore;and producing hydrocarbons from said other well bore after said steaminjecting.

References Cited UNITED STATES PATENTS 3,259,186 7/1966 Dietz 166-2633,349,849 10/ 1967 Closmann 166-285 3,354,958 11/1967 Parker 166-3033,434,544 3/ 1969 Satter et al 166-303 3,455,392 7/1969 Prats 166-30-3STEPHEN J. NOVOSAD, Primary Examiner U.S. Cl. X.R.

